Rotary positive displacement pump and method of regulating its displacement

ABSTRACT

A rotary positive displacement pump for fluids for the lubrication oil of a motor vehicle engine, has a displacement that can be regulated by the translation of a stator ring surrounding the rotor of the pump with an eccentricity depending on the position taken by the same ring due to the translation. The translation is guided by guiding fins sliding in contact with a surface of a guiding chamber, communicating with the delivery side of the pump, thanks to the fluid under pressure introduced into the same chamber and acting on the fins. The contact zone is such that a homogeneous contact pressure distribution is ensured as the operating conditions of the pump and, consequently, the position of the stator ring, vary. A method is disclosed of regulating the displacement of the pump and a lubrication system for a motor vehicle engine, in which system the pump is used.

TECHNICAL FIELD

The present invention relates to variable displacement pumps, and more particularly it concerns a rotary positive displacement pump in which the displacement variation is obtained by means of the translation of a stator ring inside which the pump rotor eccentrically rotates.

Preferably, but not exclusively, the present invention is employed in a pump for the lubrication oil of a motor vehicle engine.

PRIOR ART

It is known that, in pumps for making lubricating oil under pressure circulate in motor vehicle engines, the pump capacity, and hence the oil delivery rate, depends on the rotation speed of the engine. Hence, the pumps are designed so as to provide a sufficient delivery rate at low speeds, in order to ensure lubrication also under such conditions. If the pump has fixed geometry, at high rotation speed the delivery rate exceeds the necessary rate, giving rise to a high power absorption, and consequently to higher fuel consumption, and to a greater stress of the components due to the high pressures generated in the circuit.

In order to obviate this drawback, it is known to provide the pumps with systems allowing a delivery rate regulation at the different operating conditions of the vehicle, in particular through a displacement regulation. Different solutions are known to this aim, which are specific for the particular kind of pumping elements (external or internal gears, vanes . . . ). Some general kinds of displacement regulation systems can however be identified, and one such system is based on the translation of an element (stator ring), which is arranged in a cavity of the pump body and surrounds the rotor with an eccentricity depending on the position taken by the same ring due to its translation.

Examples of pumps of such kind are disclosed in US 2004247643, US 2008038117, WO2005068838A1 and EP 1600637.

In particular, WO2005068838A1 discloses a positive displacement pump with a vane rotor, in which the stator ring is made to slide in response to the pressure difference in two chambers located at opposite sides of the stator ring and connected to the delivery side of the pump, one chamber directly and the other one through a control valve. The translation is guided by the same members on which the pressure controlling translation acts.

This prior art pump has a number of problems that mainly affect just the ring and concern in particular:

-   -   feasibility: given the manner in which the stator ring of the         prior art pump is kept in position against the action of the         internal pressures generated by the pump operation and is guided         during translation, particular mechanical tolerances and surface         conditions are required in order to allow the proper         displacement without sticking and without leaks;     -   pressure stability: the pressure controlling the displacement of         the stator ring is the pressure at the delivery side, and this         entails that the system is considerably sensitive to the         pressure fluctuations, typical of positive displacement pumps,         present at the pump delivery side;     -   wear: due to the pressures acting on the stator ring and the         resulting sticking possibility, high wears occur between the         contacting parts in the ring and the pump body.

Pumps with a similar stator ring, originating the same problems, are disclosed in US 2004247643 and US 2008038117

It is an object of the present invention to provide a pump in which the displacement is regulated by means of the translation of the stator ring, and a method of regulating the displacement of such a pump, which obviate the drawbacks of the prior art.

DESCRIPTION OF THE INVENTION

According to the invention, this is obtained in that the stator ring includes guiding means arranged to slide in a guiding chamber formed in the pump body and preferably communicating with a pressure zone of the pump in order to receive fluid under pressure therefrom, and in that the guiding means, during the translation of the stator ring, are arranged to be pushed by the fluid under pressure into sealing contact with a surface of the guiding chamber and, in a zone of contact with such a surface, they have a curvature with such a radius that a homogeneous contact pressure distribution is ensured as the operating conditions of the pump and, consequently, the position of the stator ring, vary.

Advantageously, the guiding means comprise a pair of fins, which extend substantially tangentially to the stator ring and in opposite directions from an outer surface of the ring, define a common push surface that is acted upon by the fluid under pressure and a pair of contact areas each having the radius of curvature ensuring the homogeneous contact pressure distribution, and have rounded free ends.

In this manner, the possibility of sticking and the resulting wear are drastically reduced. Moreover, the need for sealing elements is eliminated.

The translation may be mechanically controlled, by the action of the pressures in a circuit utilising the pumped fluid, or electronically controlled, by means of a motor controlled by an electronic control unit detecting the conditions of the same fluid in a utilisation circuit.

The invention also implements a method of regulating the displacement of a rotary positive displacement pump by means of the translation of a stator ring inside which the pump rotor eccentrically rotates. According to such a method, such a translation is guided by guiding means arranged to slide in contact with a surface of a guiding chamber, formed in the pump body, due to the action of a pressurised fluid preferably coming from the delivery side of the pump, and the guiding means are made to contact the surface of the guiding chamber at a zone of the surface of the guiding means having a curvature with such a radius that a homogeneous contact pressure distribution is ensured as the operating conditions of the pump and, consequently, the position of the stator ring, vary.

According to a further aspect of the invention, there is also provided a lubrication system for a motor vehicle engine, in which the adjustable displacement pump and the method of regulating the displacement set forth above are employed.

BRIEF DESCRIPTION OF THE FIGURES

Further features and advantages of the invention will become clearly apparent from the following description of preferred embodiments, given by way of non limiting examples with reference to the accompanying drawings, in which:

FIG. 1 is an axial sectional view of a pump according to the invention;

FIG. 2 is a front view of the pump, without the front cover, showing the stator ring in the maximum displacement position;

FIGS. 3 and 4 are enlarged views of details A and B of FIG. 2;

FIGS. 5 and 6 are cross-sectional views of the pump, showing the stator ring in the maximum displacement and minimum displacement positions, respectively;

FIGS. 7 and 8 are enlarged views of details of the guiding fins of the stator ring; and

FIGS. 9 to 11 are diagrams of a lubrication circuit of a motor vehicle engine using the pump according to the invention, in different operating conditions.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIGS. 1 to 6, reference numeral 1 generally denotes a rotary positive displacement pump with adjustable displacement, in particular a pump for the lubrication oil of a motor vehicle engine, of a kind comprising a body 2 in which a chamber 3 housing a stator ring 4 is formed. Ring 4 has an internal cavity 40 in which rotor 5 eccentrically rotates and it can be translated transversally to its axis in order to regulate the pump displacement. Rotor 5 is for instance a vane rotor, vanes 6 of which are radially slidable in radial slots 7, and it is driven by a suitably shaped shaft (not shown), which is inserted in a cavity 10 of complementary shape. A centring ring 11 is mounted at each of both axially opposite ends of rotor 5 in order to keep the vanes in contact with the internal surface of ring 4 at low temperature and/or low speed.

Chamber 3 is closed by a front cover 41 and a rear cover 42. Channels 8, 9 for oil suction from the sump and oil delivery towards the oil filter, as well as lubrication channels (not shown in the drawing), are formed in rear cover 42.

Suction channel 8 communicates, through a chamber 45 in rear cover 42, with suction chambers 43, 44 formed for instance in the lower part of chamber 3 and of internal cavity 40 of the stator ring 4, respectively. Chambers 43, 44 also communicate with each other through a chamber 46 formed in front cover 41. Such a supply on both sides of the rotor of pump 1, which can also be referred to as “double supply”, allows the pump to operate in conditions of absence of cavitation up to high rotation speeds.

Oil is sent in conventional manner from suction chamber 44 to a delivery chamber 47 formed in cavity 40 and communicating in turn with delivery channel 9.

Chamber 43 preferably allows collecting possible oil leaks inside pump 1, coming from delivery chamber 47 or generally from spaces under pressure, as it will be disclosed later on.

Chamber 43, if it is located at a lower level than channel 8, also prevents the pump from emptying at the start from a stationary condition, after a long stop.

In the illustrated embodiment, the translation of ring 4, which, by way of example, is supposed to take place horizontally, is controlled by the oil pressure in the engine lubrication circuit, as it will be disclosed later on.

The translation of ring 4 is caused by a pair of substantially cylindrical push heads 13, 14, which act on two diametrically opposite areas of ring 4. Advantageously, the contacting surfaces in heads 13, 14 and ring 4 are flat surfaces, as shown in FIG. 3 for head 14. A flat contact surface does not demand special workings. A projection 12 in the wall of chamber 3 acts as a stop for the maximum displacement stroke and it is arranged to maintain, in such a condition, a certain clearance between ring 4 and rotor 5, as it is better visible in FIG. 4. The position taken by ring 4 in the condition of maximum displacement of the pump is also the reference position for mounting the ring into seat 3.

Heads 13, 14 are mounted in body 2 so as to be slidable in respective chambers 15, 16, which are closed by plugs 17 and 18 and which receive pressurised oil from the lubrication circuit of the engine either directly (chamber 16) or through a regulation valve 19 (chamber 15), also controlled by the oil pressure in the lubrication circuit.

The first push head 13 is also biased by a spring 20 that is preloaded so that head 13 keeps ring 4 in a position of maximum displacement of the pump (FIGS. 2, 5) under low oil pressure conditions, in particular at the motor start. The flat surfaces of head 13 and ring 4 in their contacting zones allow a homogeneous distribution of the force generated by spring 20 on ring 4.

The second head 14 is actuated to displace ring 4 from the maximum displacement position towards the minimum displacement position when oil pressure in chamber 16 exceeds the preload of spring 20, and it is pushed backwards by ring 4 when the latter moves back to the maximum displacement position as oil pressure in chamber 16 decreases. Thanks to a spacer 21, which may also be integrally formed with head 14, the latter is always kept in contact with ring 4 and does not adhere to plug 18.

Regulation valve 19 may be made to slide parallel to the displacement direction of ring 4, in order to manage the regulation pressures, thanks to a pair of push surfaces 19 a, 19 b which are acted upon by the oil pressure. A spring 24 tends to maintain valve 19 in the position required in order ring 4 remains in the maximum displacement position. Valve 19 may be integrated into pump body 2, in a seat 22 closed by a plug 23, as shown in FIGS. 5, 6, or in the engine block, depending on the particular engine. In any case, body 2 will be provided with seat 22 independently of the actual presence of the valve, so that a same pump body can always be utilised.

The connections of chambers 15, 16 and regulation valve 19 to the lubrication circuit will be disclosed later on.

Ring 4 is so shaped as to have a guiding member, advantageously consisting of a pair of fins 25 formed for instance in the top portion of ring 4. The fins extend substantially tangentially to the ring in opposite directions and they are housed in a guiding chamber 26 formed in body 2 and communicating with delivery channel 9. During the translation of ring 4, fins 25 slide in contact with the walls of chamber 2 and the contact is ensured by the pressure of oil picked up from delivery channel 9 and acting on top faces 27 of fins 25, defining a common push surface. The communication between delivery channel 9 and chamber 26 is obtained through a duct (not visible in the drawing) formed by means of a suitable working of rear cover 41 and/or body 2.

The shape of contact area 29 between each fin 25 and body 2 is such as to counterbalance the pressure forces generated inside the pump during operation and to maintain the contact with body 2 in a limited area in any operating condition. In this manner, there is no need for sealing elements. In particular, as shown in FIG. 7, fins 25 contact body 2 according to a curved surface having a curvature with relatively wide radius R designed so as:

-   -   to keep the contact pressure within acceptable limits         (cylinder-to-plane contact) without giving rise to upsetting of         the material in the region underneath;     -   to ensure a homogeneous contact pressure distribution as the         operating conditions vary, notwithstanding fins 25, as the         pressure applied thereto increases, bend with a consequent         displacement of the contact points.

Moreover, the free ends of fins 25 have a rounded shape, designed so as to avoid that, due to the forces exerted by the moving fins or by internal overpressures (which could bring the fins in contact with the upper surface of chamber 26, FIG. 8), ring 4 is blocked in case of an unbalance due to an overpressure surge within the pump.

Referring to FIGS. 9 to 11, lubrication circuit 100 of a motor vehicle engine 30 using pump 1 is shown. Reference numerals 31 and 32 denote the oil sump and the oil filter, connected in conventional manner to the suction and delivery channels 8 and 9 (FIG. 1), through ducts also denoted by reference numerals 8 and 9. Reference numeral 33 denotes the outlet duct of filter 12, conveying oil to engine 30. These Figures show an embodiment in which regulation valve 19 is external to pump body 2. Such an embodiment allows more clearly seeing the connections of valve 19 with lubrication circuit 100 and with the rest of pump 1.

A branch 9 a of delivery channel 9 conveys oil into chamber 26 in order to push fins 25 into contact with the base of chamber 26. As stated before, such a branch actually is a duct formed internally of the pump body. A first branch 33 a of duct 33 forms a first regulation duct conveying pressurised oil to chamber 16. A second and a third branch 33 b, 33 c of the same duct convey oil to a first and a second inlet 49 a, 49 b of valve 19. Oil fed to the first inlet 49 a preferably acts on the first push surface 19 a in order to control the possible displacement of valve 19, whereas oil fed to the second inlet 49 b may be transferred either to a second regulation duct 35, communicating with chamber 15, or to exhaust 37. The second branch 33 b conveys oil also to a distribution valve 36, for instance an electromagnetic valve. Depending on the position of this valve, oil leaving filter 32 may be conveyed, through a duct 34, to a third inlet 49 c of valve 19, where oil acts on a second push surface 19 b, or oil present in valve 19 in correspondence of inlet 49 c may be sent back to oil sump 31 (duct 38).

In accordance with other embodiments, oil fed to the first inlet 49 a and to the third inlet 49 c may act in reversed manner, for instance so that the first inlet 49 a and the third inlet 49 c act on the second push surface 19 b and the first push surface 19 a, respectively.

Thanks to the provision of distribution valve 36 and by properly dimensioning push surfaces 19 a and 19 b, it is possible to obtain two or more different intervention points for regulation valve 19.

It is to be appreciated that, depending on the requirements of the pump users, the regulation pressures (ducts 33 a and 33 c) could be taken from delivery channel 9 instead of being taken from outlet duct 33 of the filter. Yet, the illustrated solution is the solution ensuring the greatest stability in the regulation pressure since, as known, due the nature of the positive displacement pumps, the delivery pressure has surges that are smoothed by filter 32. On the contrary, it is preferable to directly take the pressure acting on fins 25 from the delivery side, in order to constantly ensure the contact between the fins and pump body 2, even if other embodiments are possible.

It is also to be appreciated that, if valve 19 is located in pump body 2, ducts 33 a, 33 b, 34 35 will be formed, at least in part, in body 2 by means of a suitable working, in similar manner to what has been stated for the duct putting delivery channel 9 in communication with chamber 26.

The operation of pump 1 is as follows.

When the motor is started, there is a low oil pressure at the delivery side and the pump is in the maximum displacement condition (FIG. 9). Under such a condition, the preload of spring 24 pushes valve 19 wholly to the left, so that oil can pass from inlet 49 b to duct 35 and hence into chamber 15. In opposition to the reaction produced by the pressure sent into that chamber, the first regulation duct 33 a picks up pressure downstream filter 32 and sends it to chamber 16. Due to a force balance in the direction in which push heads 13, 14 act, ring 4 is in contact with mechanical stop 12 (FIGS. 2, 3).

During the operation of pump 1, the pressure at outlet 33 from filter 32 (and hence at inlet 49 a of valve 19) increases and, once it has exceeded a given threshold, it overcomes the preload of spring 24, thereby making valve 19 displace to the right. The displacement of valve 19 progressively closes inlet 49 b and puts chamber 15 in communication with exhaust 37. In this manner, the pressure in chamber 15 decreases and the pressure in chamber 16 can overcome the preload of spring 21 and displace ring 4 proportionally to the pressure drop in chamber 15. Of course, the displacement of ring 4 ends when the minimum displacement position is reached (FIG. 10).

As the pressure in duct 33 decreases, it is possible to resume the maximum displacement position thanks to the displacement of valve 19 to the left caused by spring 24. By such a displacement, the communication between inlet 49 b and regulation duct 35 is restored and the pressure always present in chamber 16 can no longer overcome the combined action of the pressure in chamber 15 (which pressure is being progressively restored) and of spring 21.

If an intervention of valve 19 at a pressure level different from the high pressure level described above is desired, electromagnetic valve 36 will be actuated so as to apply the pressure existing at outlet 33 of filter 32 also to inlet 49 c of valve 19 (FIG. 11). The push is now exerted on both push surfaces 19 a, 19 b and hence the preload of spring 20 can be overcome by a pressure lower than the previous one. It is clear for the skilled in the art that valve 36 also allows obtaining also multiple actuation levels different from the high pressure level for regulation valve 19.

Thanks to the peculiar shape of ring 4, the invention actually solves the problems mentioned above of the prior art.

Indeed, the mechanical and/or geometrical tolerances and the surface conditions suitable for ensuring the proper sliding of ring 4 only concern the small contact zone between ring 4 and body 2 (that is, between fins 25 and guide 26), whereas the whole remaining surface of the fins may remain raw. Also a special working of the ring surface zones in contact with push heads 13, 14 is not required. This allows reducing the manufacturing costs.

Moreover, the wide radius R in zone 28 allows reducing the contact pressure and, as the pressure acting on ring 4 varies during operation, it allows displacing the contact point while keeping the shape of the contact pressure distribution constant. This prevents sticking and wear of the parts in relative movement, always possible in the prior art. Also the rounded shapes of the ends of fins 25 contribute to avoiding sticking during the normal sliding of ring 4 or during possible unbalances of same due to overpressure surges inside the pump.

On the other hand, the constant contact between fins 25 and body 2 eliminates the need for sealing elements in order to avoid excessive oil leaks, thereby contributing to the constructional simplicity and hence to the limitation of the manufacturing costs. The lack of sealing elements moreover assists in having a faster system response to the displacement variation signal.

It is clear that the above description has been given only by way of non-limiting example and that changes and modifications are possible without departing from the scope of the invention.

For instance, even if in the illustrated embodiment the displacement of ring 4 is mechanically controlled by the pressures in the lubrication circuit, an electronic control is also possible, through a small electric motor (brushless, three-phase synchronous or step-by-step motor) directly connected to ring 4 through a lever system, a mechanical coupling or another linkage arranged to convert the rotary movement of the motor into a translatory movement. The motor will be electronically controlled by the electronic control unit of the motor vehicle, thereby ensuring a greater accuracy and a greater readiness in the intervention. The advantage of this solution is related to the possibility of having a continuous displacement variation in any condition of use, at any speed and temperature at infinite pressure levels.

Lastly, even if the invention has been disclosed in detail with reference to a pump for the lubrication oil of a motor vehicle engine, it may be applied to any positive displacement pump for conveying fluid from a first to a second working environment, in which a delivery rate reduction as the pump speed increases is convenient 

1-11. (canceled)
 12. A rotary positive displacement pump for fluids, comprising a rotor arranged to eccentrically rotate in a chamber defined within a stator ring, which is located in a seat formed in a pump body and is connected to means for translating such a ring relative to the rotor, as the operating conditions of the pump vary, in order to change the pump displacement, wherein the stator ring includes guiding means arranged to slide in a guiding chamber formed in the pump body and communicating with a pressure zone of the pump or with utilisation devices of a pumped fluid, in order to receive fluid under pressure therefrom, characterised in that the guiding means, during the translation of the stator ring, are arranged to be pushed by the fluid under pressure into sealing contact with a surface of the guiding chamber and, in a zone of contact with such a surface, they have a curvature with such a radius of curvature that a homogeneous contact pressure distribution is ensured as the operating conditions of the pump and, consequently, the position of the stator ring, vary.
 13. The pump as claimed in claim 12, wherein the guiding means comprise a pair of oppositely directed fins extending substantially tangentially to the stator ring from an outer surface of the stator ring and defining a common push surface that is acted upon by the fluid under pressure and a pair of contact areas each having said curvature with such a radius of curvature that the homogeneous contact pressure distribution is ensured.
 14. The pump as claimed in claim 13, wherein the fins have rounded free ends.
 15. The pump as claimed in claim 12, wherein the translation of the stator ring is controlled by a first and a second push head, which act on diametrically opposite areas of the ring and are arranged to slide in a first and a second push chamber, respectively, which chambers are distinct from the guiding chamber and communicate with the pressure zone of the pump or, preferably, with the utilisation devices of the pumped fluid, through a regulation valve or directly, respectively.
 16. The pump as claimed in claim 13, wherein the translation of the stator ring is controlled by a first and a second push head, which act on diametrically opposite areas of the ring and are arranged to slide in a first and a second push chamber, respectively, which chambers are distinct from the guiding chamber and communicate with the pressure zone of the pump or, preferably, with the utilisation devices of the pumped fluid, through a regulation valve or directly, respectively.
 17. The pump as claimed in claim 15, wherein the regulation valve is integrated in the pump.
 18. The pump as claimed in claim 16, wherein the regulation valve is integrated in the pump.
 19. The pump as claimed in claim 15, wherein the push heads are arranged to separate a suction environment of the pump from a high pressure environment where the guiding means slide.
 20. The pump as claimed in claim 16, wherein the push heads are arranged to separate a suction environment of the pump from a high pressure environment where the guiding means slide.
 21. The pump as claimed in claim 17, wherein the push heads are arranged to separate a suction environment of the pump from a high pressure environment where the guiding means slide.
 22. The pump as claimed in claim 12, wherein the translation of the stator ring is controlled by an electric motor.
 23. The pump as claimed in claim 13, wherein the translation of the stator ring is controlled by an electric motor.
 24. The pump as claimed in claim 12, wherein the pump is a pump for the lubrication circuit of an engine of a motor vehicle.
 25. A method of regulating the displacement of a rotary positive displacement pump, comprising the steps of: translating, relative to a rotor of the pump, a stator ring inside which the rotor eccentrically rotates; guiding the translation of the stator ring through guiding means arranged to slide in a guiding chamber formed in a pump body and communicating with a pressure zone of the pump or with utilisation devices of the pumped fluid; the method being characterised in that it further comprises the steps of: making the pumped fluid act upon the guiding means in order to keep them in sealing contact with a surface of the guiding chamber during the translation of the stator ring; and making the guiding means contact the surface of the guiding chamber at a zone of the surface of the guiding means having a curvature with such a radius of curvature that a homogeneous contact pressure distribution is ensured as the operating conditions of the pump and, consequently, the position of the stator ring, vary.
 26. The method as claimed in claim 25, for regulating the displacement of a pump for the lubrication oil for the engine of a motor vehicle.
 27. A lubrication system for an engine of a motor vehicle, comprising a pump according to claim
 12. 